1. Description of the Invention
This invention relates to motion picture projectors and in particular to a motion picture projector designed for edgewise loading of the film.
2. Description of the Prior Art
In the past, a great majority of the motion picture projectors that have been produced required the film to be manually "threaded", that is, passed around a number of tooth sprockets, through the film shuttle, and, in the case of a projector provided with an audio amplifier, around a sound drum, while placing the perforations in the film in mesh with the teeth of the appropriate sprockets and then closing the guide members which hold the film into contact with the sprockets. It also is necessary to manually establish loops of the correct lengths between the drive sprockets on either side of the film shuttle intermittent advancement mechanism.
In practice, it sometimes is found that threading of the film in a projector of this type is a complicated and difficult operation. If the film is threaded incorrectly, it is likely to be damaged and cause unsatisfactory performance of the projector.
In order to overcome this difficulty of manual threading of the film, many "self threading" projectors have been produced in an attempt to alleviate the above noted difficulties. In a self threading projector, the end of the film is introduced endwise into a slot which then leads it to a first tooth sprocket which engages the film perforations and drives it forward when the mechanism is in motion. The end of the film strip is guided by a series of curved members which force it to travel in succession to another part of the film drive system where it is engaged successively by various driving members and sprockets. When the leading end of the film has been carried through a complete threading path, it emerges from the mechanism and is attached to a takeup reel. In order to operate a projector of this type, it is necessary to withdraw loop forming guides so that the film loops can move freely adjacent the film shuttle.
These self threading projectors have several disadvantages. Particularly, successful engagement of the perforations in the film with each of the sprockets depends on the condition of the end of the film strip. The end of the strip must not have sharp bends near the leading end region (such as its often produced when the film is attached to a takeup reel) or the film will not properly be fed through the projector. If the film is not in good condition, it is likely to be damaged further by the first sprocket in the projector to such an extent that it will become jammed at some later point in its path.
While self threading mechanisms of this type have been used with some success on motion picture projectors which do not include audio amplifiers, it is much more difficult to make the projector operate successfully when it is necessary to wrap a sound drum because of the more complicated film path required to be established about the sound drum.
Additionally, in both of the above mentioned types of projectors, once the film has been threaded into the projector, it is possible to remove the film only by running the projector until one of the ends of the film passes completely through the projector. Therefore, if it is desired to show only a portion of a movie (e.g., a segment in the middle thereof), a substantially large amount of time is wasted as the film strip is driven through the projector until the desired beginning point is reached and likewise after the desired portion has been viewed by the user.